The most common type of lock in use at the present time, particularly on door latches in buildings, is the tumbler pin lock. Such a lock usually includes a lock cylinder housing with a cylindrical bore extending longitudinally therethrough, a cylindrical core positioned rotatably in the bore and having a longitudinal keyway therein for receiving a key bit. A plurality of top pin chambers are positioned in the cylinder housing perpendicular to and extending radially outward from the cylindrical bore, and correspondingly spaced bottom pin chambers are positioned in the core. Top pins are generally positioned in the top pin chambers, and bottom pins are generally positioned in the bottom pin chambers, although top pins can move partially into bottom chambers and bottom pins can move partially into top chambers when the core is rotated to align corresponding top and bottom chambers with each other. In fact, a pin positioned partially in a top pin chamber are partially in a bottom pin chamber across the shear plane between the cylinder housing and the rotatable core prohibits the core from being rotated and provides the locking effect of the lock mechanism.
Typically, the lengths of the individual bottom pins are selected to establish the keying requirements of the lock. In order for a key to open the lock, it must have a key bit with bitting and spacing thereon cut to correspond inversely to the bottom pin lengths. The fitting must be cut and spaced such that when the key is inserted into the keyway the bitting acts on the bottom pins to align all of the interfaces between the top pins and bottom pins respectively with the shear plane between the core and the cylinder housing. When all of the interfaces between the top and bottom pins are aligned with the shear plane, the core can be turned to operate a lock or latch mechanism. However, if a properly cut key bit is not positioned in the core, at least one top tumbler pin is positioned across the shear plane, and the core cannot be rotated within the cylinder housing.
Master key arrangements are also available in such conventional cylinder locks. For example, a plurality of cylinder locks can be provided, each lock having a separate keying arrangement that requires a unique key bit to open the lock, as well as being openable by a common master key that is capable of opening all of the locks in the set. Such master key lock devices are basically of the same construction as that described above, with the exception that master wafers or spacers are positioned between one or more of the top and bottom pin sets to provide more than one interfacing surface for alignment with the shear plane. For example, one master wafer positioned between a top and a bottom pin in such a lock provides one potential interface at the top of the wafer and another potential interface at the bottom of the wafer. The master key can be provided with bitting and spacing to align the interface at the bottom of the master wafer with the shear plane in order to rotate the core, and a different individual key can be provided with bitting and spacing to align the interface at the top of the wafer with the shear plane to also rotate the core.
When one desires to rekey such conventional cylinder locks, the cylinder and core must be disassembled, the bottom pins removed are replaced with a different set of bottom pins of different selected lengths. Such a process is time consuming and usually requires the services of a locksmith to perform properly. Unfortunately, there are situations in which rekeying is required quite often. For example, in apartments and office buildings, there may be frequent turnover of tenants, which requires frequent lock changes. In some other security applications, locks are changed periodically as a matter of policy. In such applications, the cost of rekeying can be a significant expense. A method and apparatus for rekeying such locks easily and without disassembly could substantially reduce the cost and inconvenience of rekeying locks.